1. Field Of The Invention
The present invention relates generally to straddle packer apparatus for isolating a zone of a well, and more particularly, but not by way of limitation, to straddle packer apparatus capable of being lowered through a production tubing on a coiled tubing, and then inflated to isolate a zone of a production casing for treatment without the need for pulling the production tubing from the well.
2. Description Of The Prior Art
During the life of an oil or gas well, it is often desirable to perform treating operations on some subsurface zone of the well. The cost involved in performing treating operations on completed wells which require the removal of production tubing is often very high. This is especially true when a well is located in a remote area such as the North Slope of Alaska where a drilling rig must be moved back over the well in order to perform work over operations. Many of these wells located on the North Slope of Alaska are equipped with large tubing strings, e.g., three inch or four and one-half inch tubing, production packers and gas lift valves. This high work over cost creates the need for tools which can be run on small diameter coiled tubing and can pass through production tubing and other equipment and then expand out to seal off intervals inside the production casing for treating operations.
The prior art presently includes several straddle packer apparatus which can be utilized in the general manner described above. A first such device is being marketed by Nowsco Well Service Ltd. of Aberdeen, Scotland, as described in an Ocean Industry article dated February, 1989, entitled "Thru-Tubing Straddle Packer Expands, Seals in Casing" at pages 44-45. That apparatus is lowered into the well while circulating fluid down through the coiled tubing and out a dump sub. After the tool is located at the appropriate position in the well, the pumping rate down the coiled tubing is increased and the dump sub closes thus directing fluid to the packers to inflate the packers. Weight is then set down on the apparatus to close the inflation ports and open the treating ports. After treatment is completed picking up weight reopens the packer inflation ports and allows the packers to deflate. The tool can then be relocated and recycled to treat another zone.
Another inflatable straddle packer is marketed by Tam International of Houston, Texas, as disclosed in the Tam International 1980-1981 General Catalog under the heading "Inflatable Perforation Wash Tool". The Tam International inflatable perforation wash tool can be run on coiled tubing. A ball is dropped to seal the mandrel of the tool prior to inflation of the packers. Weight is then set down on the tool to close the inflation ports and open the circulating or treating ports. After treatment, weight is picked up to deflate the packers and unseat the tool.
U.S. Pat. No. 4,648,448 to Sanford et al., and assigned to Tam International, Inc., of Houston, Tex., discloses another straddle packer apparatus. The apparatus disclosed in the '448 patent utilizes a lug and J-slot structure which is actuated by a combination of reciprocation and rotation of a rigid tubing string on which the tool is lowered. When run on a rigid tubing string, so that the tool can be rotated to actuate the J-slot mechanism, it does not appear that this apparatus could be run through production tubing and set in production casing below the production tubing. A Tam International advertising brochure entitled "Tam-J.TM. Inflatable Workover/Testing Packers And Accessories Ordering Guide" dated January, 1986, indicates at page 5 thereof under the heading "Coil-Tubing Operations" that smaller diameter Tam-J.TM. packers can be utilized on continuous coil tubing by removing the lugs from the J-slot mechanism and allowing the tool to be set, released and reset with straight up and down movement of the coil tubing. Thus, the J-slot mechanism is in effect eliminated from this straddle packer apparatus when it is utilized with coil tubing, which cannot be rotated.
All of the devices discussed above which are designed to be run on coiled tubing down through production tubing and then set in production casing are limited in their operating flexibility since they only have two operating positions which are achieved by either setting down weight or picking up weight. These tools are run into the well with their inflating ports in an open position, and after being located at the appropriate elevation in the well, the packers are inflated to seal them against the casing. Weight is then set down on the packers to close the inflation ports and open a treating port between the packers. Subsequently, weight is picked up from the apparatus to close the treating ports and reopen the inflation ports thus allowing the packers to deflate.